[milo] log when user gets access denied to a git project.
[milo] log when user gets access denied to a git project.

R=2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org

Change-Id: Ibc896327b2bd4aa2e0ef632d0317f93e7726b918
Reviewed-on: https://chromium-review.googlesource.com/1088232
Reviewed-by: Ryan Tseng <2190fe9a39b4920ec7bd59c848ec5cccd163056f@chromium.org>
Commit-Queue: Andrii Shyshkalov <a30c74fa30536fe7ea81ed6dec202e35e149e1fd@chromium.org>

luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go,luci/luci-go